1. Field of the Invention
The present invention relates to a differential steering type motorized vehicle having a pair of right and left drive wheels to be drive-controlled so as to perform differential steering according to the difference in the rotational direction and the rotational speed at a central position between a front wheel and rear wheels.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Application Publication No. 8-154301 or the like, a motorized three-wheeler is known, which is used as a golf cart or a motorized three-wheeler for physically handicapped persons or aged persons with leg disabilities. In such a motorized three-wheeler, a front wheel located at a central position along the lateral axis direction can be steered directly by turning handlebars via a handlebar shaft, and right and left rear wheels are driven by a motor with a battery as a power supply.
As disclosed in Japanese Unexamined Patent Application Publication No. 47-12461, an omnidirectional movable vehicle is known, which is equipped with wheels having rotating bodies, i.e., rollers, arrayed around hubs, each of the rotating bodies having an axis of rotation inclined obliquely in the forward-advancing direction. Using these wheels, the vehicle is turnable on the spot by 360° and movable laterally using a differential steering type four-wheel drive. In addition, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-137602, a nonturning omnidirectional wheel is known, which has a roller with a half-spindle shape, and as disclosed in Japanese Unexamined Patent Application Publication No. 2005-47312, a differential steering type omnidirectional movable vehicle is known, which is driven with the torque and rotational direction of four wheels being independent from each other by inclining the wheels having the rollers with the half-spindle shape symmetrically in the forward-advancing direction.
In Japanese Unexamined Patent Application Publication No. 9-294779, a four-wheel differential steering type wheelchair is disclosed, which is provided with a pair of right and left front wheels to be steered from a parallel state independently from each other to various kinds of non-parallel states, and a pair of right and left rear wheels to be motorized in a differential rotating manner independently from each other, and capable of performing on-the-spot turning by setting the front wheels in a V-shape, and rotating one rear wheel in the reverse direction at a same speed with respect to the other rear wheel in a private house, a hospital or the like.
On the other hand, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-104397, a six-wheel differential steering type motorized wheelchair is known, which is provided with an elevating/lowering seat, a pair of right and left drive wheels to be controlled in a differential rotating manner at a central position in the longitudinal axis, a pair of right and left front wheels, and a pair of right and left rear wheels, and capable of performing standing work in a seated state by elevating the seat, and performing on-the-spot turning.
The motorized three-wheeler disclosed in the above-described Japanese Unexamined Patent Application Publication No. 8-154301 can be steered by handlebar operation of the front wheel, and the steering method therefor is familiar even to aged persons. However, the operation of directional change without any advancing, i.e., on-the-spot turning cannot be performed. The four-wheel drive differential steering type motorized vehicles disclosed in the above-described Japanese Unexamined Patent Application Publication No. 47-12461, and Japanese Unexamined Patent Application Publication No. 2005-47312 can perform spin-like on-the-spot turning around a central position of four wheels, i.e., around a part in a vicinity of the central position of a vehicle body. However, their driving mechanisms are expensive, and their steering method is based not on direct steering of the wheels, but on electronic control by an operation unit such as a joystick for generating a steering command signal, which is difficult for aged persons to use in comparison with that of the handlebar operation type; and a problem occurs, in that excessively large or small steering easily occurs unless the aged persons become sufficiently adept at steering. In the wheelchair capable of performing on-the-spot turning disclosed in the above-described Japanese Unexamined Patent Application Publication No. 9-294779, swing-like on-the-spot turning is performed around the central position between the right and left rear wheels in differential rotation, i.e., around a rear portion of the vehicle body as the center of rotation.
On the other hand, the six-wheel differential steering type motorized wheelchair disclosed in Japanese Unexamined Patent Application Publication No. 2001-104397 can perform spin-like on-the-spot turning around the central position of the right and left drive wheels in differential rotation, i.e., around the central position of the vehicle body. However, it is not assumed in this case that the front and rear wheels are of the nonturning type, and the wheelchair moving in the moving direction easily becomes unstable before the wheelchair follows the steering direction. In addition, in the steering of the wheelchair, the right and left drive wheels are subjected to differential rotation type control in response to the steering command signal to be output by the operation of the operation unit, and the wheels are not driven directly by the handlebar operation, resulting in problems of familiarity with the operational method or steering characteristics as described above.